In order to use palm oil for food, usually, palm oil is refined by subjecting it to degumming, deacidification, decolorization and deodorization. In general, refined palm oil is estimated as an oil having excellent stability to oxidation. However, refined palm oil has a problem that, when it is used for cooking, for example, fries or the like, browning is quickly taken place (color reversion) and is not faded. That is, some of users complain that color reversion is deterioration of quality. And, since food obtained by cooking with color reversed palm oil becomes brownish, some of products are decreased their commercial value.
On the other hand, flavor of color reversed palm oil and cooked food using it have hardly changed. Therefore, there are hitherto few reports of studies on improvement of color reversion. For example, J.A.O.C.S., Vol. 59, No. 3 (March 1982) 129-131 reports a relation between acidity of an activated clay as a decolorizing agent and capability of decolorizing palm oil. However, this decolorization capability is intended to improve a color tone of refined oil itself and not to improve color reversion upon using it for cooking afterwards. According to a result of the present inventors' study, any relation between acidity of an activated clay and color reversion has been hardly observed.